The present invention relates to a pattern formation method for use in fabrication process or the like for semiconductor devices.
In accordance with the increased degree of integration of semiconductor integrated circuits and downsizing of semiconductor devices, there are increasing demands for further rapid development of lithography technique. Currently, pattern formation is carried out through photolithography using exposing light of a mercury lamp, KrF excimer laser, ArF excimer laser or the like, and use of F2 laser lasing at a shorter wavelength is being examined. However, since there remain a large number of problems in exposure systems and resist materials, photolithography using exposing light of a shorter wavelength has not been put to practical use.
In these circumstances, it is regarded significant to increase the life time of ArF excimer laser lithography, and resists for use in the ArF excimer laser lithography are now being developed.
Some of such ArF resists have a lactone ring in the composition of a polymer included therein (for example, see T. Kudo et al., “Illumination, Acid Diffusion and Process Optimization Considerations for 193 nm Contact Hole Resists”, Proc. SPIE, vol. 4690, p. 150 (2002)). This is because a lactone ring is expected to improve the adhesion or the like of a resist pattern onto a target film (i.e., a film to be etched by using the resist pattern).
Now, a conventional pattern formation method will be described with reference to FIGS. 5A through 5D, 6A and 6B.
First, a positive chemically amplified resist material having the following composition is prepared:
Base polymer: poly(2-methyl-2-adamantyl methacrylate   2 g(50 mol %) - γ-butyrolactone methacrylate (40 mol %) -2-hydroxy adamantane methacrylate (10 mol %))Acid generator: triphenylsulfonium trifluoromethane sulfonate 0.06 gQuencher: triethanolamine0.002 gSolvent: propylene glycol monomethyl ether acetate  20 g
Next, as shown in FIG. 5A, the aforementioned chemically amplified resist material is applied on a substrate 1 of silicon oxide so as to form a resist film 2 with a thickness of 0.35 μm.
Then, as shown in FIG. 5B, pattern exposure is carried out by irradiating the resist film 2 with exposing light 4 of ArF excimer laser of a wavelength of 193 nm with NA of 0.68 through a mask 3.
After the pattern exposure, as shown in FIG. 5C, the resist film 2 is baked with a hot plate at a temperature of 105° C. for 60 seconds, and the resultant resist film is developed with a 0.26 N tetramethylammonium hydroxide developer. In this manner, a resist pattern 2a made of an unexposed portion of the resist film 2 and having an opening width of 0.09 μm is formed as shown in FIG. 5D.
Next, as shown in FIG. 6A, the substrate 1 is etched with fluorine radicals with the resist pattern 2a used as a mask. At this point, FIG. 6A is a cross-sectional view of the substrate 1 and FIG. 6B is a plan view of the substrate 1 on which the resist pattern 2a is formed. As shown in FIG. 6B, a recess 1a having an opening width of 0.09 μm is formed in the substrate 1 through this etching.
However, as shown in FIG. 6B, the recess 1a formed in the substrate 1 by the conventional pattern formation method is in a defective shape with an irregular wall.